1. Field of the Invention
This invention generally relates to remote communications for systems such as remote keyless entry systems. More particularly, this invention relates to secure synchronization for facilitating remote control communications.
2. Description of the Prior Art
Many remote control systems such as remote keyless entry systems use rolling code schemes to prevent code capturing that would allow an unauthorized individual to gain access to the system. Typical rolling code schemes rely upon a synchronization counter that is incremented on each new transmitted command by the remote signaling device. In some situations, the synchronization counter value is used as an input into an encryption algorithm to generate a rolling code. The receiving unit that receives the command must have the synchronization counter at the same value or within an acceptable window, depending on the particular system. If the synchronization counter of the remote signaling device and the receiving device do not match or sufficiently correspond, an authorized transmission is not received and handled as a valid transmission. One example situation where the synchronization counters may not match is when a remote signaling device is continually activated (purposefully or accidentally) outside the range of the receiver so that the counter on the remote signaling unit is repeatedly incremented while the counter on the receiving unit is not.
It is not acceptable to overcome the difficulty of unmatching synchronization counter values by simply transmitting the synchronizer counter value from the remote transmitting unit in a fully open state, because that allows it to be susceptible to unauthorized signal capture, which is the entire point of utilizing a synchronization counter. Accordingly, open transmission of the synchronization counter information defeats the purpose of utilizing the synchronization counter.
There is a need for being able to continue communications between a remote signaling unit and a receiver that rely upon matching synchronization counter values to establish effective, secure communication.
This invention addresses the need for re-establishing synchronization where a remote signaling device and a receiver are otherwise incapable of utilizing secure communication that is based at least in part on corresponding synchronization counter values.